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<p>Converts between types by reinterpreting the underlying bit pattern.
</p>
<table id="toc" class="toc"><tr><td>
<div id="toctitle"><h2>Contents</h2></div>
<ul>
<li class="toclevel-1 tocsection-1"><a href="reinterpret_cast.html#Syntax"><span class="tocnumber">1</span> <span class="toctext">Syntax</span></a></li>
<li class="toclevel-1 tocsection-2"><a href="reinterpret_cast.html#Explanation"><span class="tocnumber">2</span> <span class="toctext">Explanation</span></a></li>
<li class="toclevel-1 tocsection-3"><a href="reinterpret_cast.html#Keywords"><span class="tocnumber">3</span> <span class="toctext">Keywords</span></a></li>
<li class="toclevel-1 tocsection-4"><a href="reinterpret_cast.html#Type_aliasing"><span class="tocnumber">4</span> <span class="toctext">Type aliasing</span></a></li>
<li class="toclevel-1 tocsection-5"><a href="reinterpret_cast.html#Notes"><span class="tocnumber">5</span> <span class="toctext">Notes</span></a></li>
<li class="toclevel-1 tocsection-6"><a href="reinterpret_cast.html#Example"><span class="tocnumber">6</span> <span class="toctext">Example</span></a></li>
<li class="toclevel-1 tocsection-7"><a href="reinterpret_cast.html#See_also"><span class="tocnumber">7</span> <span class="toctext">See also</span></a></li>
</ul>
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<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Syntax">edit</a>]</span> <span class="mw-headline" id="Syntax">Syntax</span>
</h3>
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<td class="t-sdsc-nopad"> <code><b>reinterpret_cast &lt;</b></code> <span class="t-spar">new_type</span> <code><b>&gt; (</b></code> <span class="t-spar">expression</span> <code><b>)</b></code>
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<p>Returns a value of type <code>new_type</code>.
</p>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Explanation">edit</a>]</span> <span class="mw-headline" id="Explanation">Explanation</span>
</h3>
<p>Unlike <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span></span></span>, but like <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">const_cast</span></span></span>, the <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">reinterpret_cast</span></span></span> expression does not compile to any CPU instructions. It is purely a compiler directive which instructs the compiler to treat the sequence of bits (object representation) of <span class="t-spar">expression</span> as if it had the type <span class="t-spar">new_type</span>.
</p>
<p>Only the following conversions can be done with <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">reinterpret_cast</span></span></span>, except when such conversions would cast away <i>constness</i> or <i>volatility</i>.
</p>
<div class="t-li1">
<span class="t-li">1)</span> An expression of integral, enumeration, pointer, or pointer-to-member type can be converted to its own type. The resulting value is the same as the value of <code>expression</code>. <span class="t-mark-rev t-since-cxx11">(since C++11)</span>
</div>
<div class="t-li1">
<span class="t-li">2)</span> Any pointer can be converted to any integral type large enough to hold the value of the pointer (e.g. to <span class="t-lc"><a href="../types/integer.html" title="cpp/types/integer">std::uintptr_t</a></span>)</div>
<div class="t-li1">
<span class="t-li">3)</span> A value of any integral or enumeration type can be converted to a pointer type. A pointer converted to an integer of sufficient size and back to the same pointer type is guaranteed to have its original value, otherwise the resulting pointer cannot be dereferenced safely (the round-trip conversion in the opposite direction is not guaranteed; the same pointer may have multiple integer representations) The null pointer constant <span class="t-lc"><a href="../types/NULL.html" title="cpp/types/NULL">NULL</a></span> or integer zero is not guaranteed to yield the null pointer value of the target type; <a href="static_cast.html" title="cpp/language/static cast">static_cast</a> or <a href="implicit_cast.html" title="cpp/language/implicit cast">implicit conversion</a> should be used for this purpose.</div>
<div class="t-li1">
<span class="t-li">4)</span> Any value of type <span class="t-lc"><a href="../types/nullptr_t.html" title="cpp/types/nullptr t">std::nullptr_t</a></span>, including <span class="t-c"><span class="mw-geshi cpp source-cpp">nullptr</span></span> can be converted to any integral type as if it were <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span><span class="kw4">void</span><span class="sy2">*</span><span class="br0">)</span><span class="nu0">0</span></span></span>, but no value, not even <span class="t-c"><span class="mw-geshi cpp source-cpp">nullptr</span></span> can be converted to <span class="t-lc"><a href="../types/nullptr_t.html" title="cpp/types/nullptr t">std::nullptr_t</a></span>: <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span></span></span> should be used for that purpose. <span class="t-mark-rev t-since-cxx11">(since C++11)</span>
</div>
<div class="t-li1">
<span class="t-li">5)</span> Any pointer to object of type <code>T1</code> can be converted to pointer to object of another type <i>cv</i> <code>T2</code>. This is exactly equivalent to <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1">&lt;</span>cv T2<span class="sy2">*</span><span class="sy1">&gt;</span><span class="br0">(</span><span class="kw1">static_cast</span><span class="sy1">&lt;</span>cv <span class="kw4">void</span><span class="sy2">*</span><span class="sy1">&gt;</span><span class="br0">(</span>expression<span class="br0">)</span><span class="br0">)</span></span></span> (which implies that if <code>T2</code>'s alignment requirement is not stricter than <code>T1</code>'s, the value of the pointer does not change and conversion of the resulting pointer back to its original type yields the original value). In any case, the resulting pointer may only be dereferenced safely if allowed by the <i>type aliasing</i> rules (see below) </div>
<div class="t-li1">
<span class="t-li">6)</span> An lvalue expression of type <code>T1</code> can be converted to reference to another type <code>T2</code>. The result is an lvalue or xvalue referring to the same object as the original lvalue, but with a different type. No temporary is created, no copy is made, no constructors or conversion functions are called. The resulting reference can only be accessed safely if allowed by the <i>type aliasing</i> rules (see below)</div>
<div class="t-li1">
<span class="t-li">7)</span> Any pointer to function can be converted to a pointer to a different function type. Calling the function through a pointer to a different function type is undefined, but converting such pointer back to pointer to the original function type yields the pointer to the original function.</div>
<div class="t-li1">
<span class="t-li">8)</span> On some implementations (in particular, on any POSIX compatible system as required by <a rel="nofollow" class="external text" href="http%3A//pubs.opengroup.org/onlinepubs/9699919799/functions/dlsym.html">dlsym</a>), a function pointer can be converted to <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span> or any another object pointer, or vice versa. If the implementation supports conversion in both directions, conversion to the original type yields the original value, otherwise the resulting pointer cannot be dereferenced or called safely.</div>
<div class="t-li1">
<span class="t-li">9)</span> The null pointer value of any pointer type can be converted to any other pointer type, resulting in the null pointer value of that type. Note that the null pointer constant <span class="t-c"><span class="mw-geshi cpp source-cpp">nullptr</span></span> or any other value of type <span class="t-lc"><a href="../types/nullptr_t.html" title="cpp/types/nullptr t">std::nullptr_t</a></span> cannot be converted to a pointer with <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">reinterpret_cast</span></span></span>: implicit conversion or <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span></span></span> should be used for this purpose.</div>
<div class="t-li1">
<span class="t-li">10)</span> An rvalue pointer to member function can be converted to pointer to a different member function of a different type. Conversion to the original type yields the original value, otherwise the resulting pointer cannot be used safely.</div>
<div class="t-li1">
<span class="t-li">11)</span> An rvalue pointer to member object of some class <code>T1</code> can be converted to a pointer to another member object of another class <code>T2</code>. If <code>T2</code>'s alignment is not stricter than <code>T1</code>'s, conversion to the original type yields the original value, otherwise the resulting pointer cannot be used safely.</div>
<p>As with all cast expressions, the result is:
</p>
<ul>
<li> an lvalue if <span class="t-spar">new_type</span> is an lvalue reference type or an rvalue reference to function type;
</li>
<li> an xvalue if <span class="t-spar">new_type</span> is an rvalue reference to object type; 
</li>
<li> a prvalue otherwise.
</li>
</ul>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Keywords">edit</a>]</span> <span class="mw-headline" id="Keywords">Keywords</span>
</h3>
<p><a href="../keyword/reinterpret_cast.html" title="cpp/keyword/reinterpret cast"><tt>reinterpret_cast</tt></a>
</p>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Type aliasing">edit</a>]</span> <span class="mw-headline" id="Type_aliasing">Type aliasing</span>
</h3>
<p>When a pointer or reference to object whose <a href="incomplete_type.html#Dynamic_type" title="cpp/language/type">dynamic type</a> is <code>DynamicType</code> is <code>reinterpret_cast</code> (or <a href="explicit_cast.html" title="cpp/language/explicit cast">C-style cast</a>) to a pointer or reference to object of a different type <code>AliasedType</code>, the cast always succeeds, but the resulting pointer or reference may only be used to access the object if both <code>DynamicType</code> and <code>AliasedType</code> are <a href="../concept/StandardLayoutType.html" title="cpp/concept/StandardLayoutType">standard-layout types</a> and one of the following is true:
</p>
<ul><li> <code>AliasedType</code> is the (possibly <a href="cv.html" title="cpp/language/cv">cv</a>-qualified) <code>DynamicType</code>
</li></ul>
<ul><li> <code>AliasedType</code> and {<code>DynamicType</code> are both (possibly multi-level, possibly cv-qualified at each level) pointers to the same type <code>T</code> <span class="t-mark-rev t-since-cxx11">(since C++11)</span>
</li></ul>
<ul><li> <code>AliasedType</code> is the (possibly <a href="cv.html" title="cpp/language/cv">cv</a>-qualified) signed or unsigned variant of <code>DynamicType</code>
</li></ul>
<ul><li> <code>AliasedType</code> is an <a href="aggregate_initialization.html" title="cpp/language/aggregate initialization">aggregate type</a> or a <a href="union.html" title="cpp/language/union">union</a> type which holds one of the aforementioned types as an element or non-static member (including, recursively, elements of subaggregates and non-static data members of the contained unions): this makes it safe to obtain a usable pointer to a struct or union given a pointer to its non-static member or element.
</li></ul>
<ul><li> <code>AliasedType</code> is a (possibly <a href="cv.html" title="cpp/language/cv">cv</a>-qualified) <a href="derived_class.html" title="cpp/language/derived class">base class</a> of <code>DynamicType</code>
</li></ul>
<ul><li> <code>AliasedType</code> is <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char</span></span></span> or <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">char</span></span></span>: this permits examination of the  <a href="objects.html#Object_representation_and_value_representation" title="cpp/language/object">object representation</a> of any object as an array of unsigned char.
</li></ul>
<p>If <code>AliasedType</code> does not satisfy these requirements, accessing the object through the new pointer or reference invokes <a href="ub.html" title="cpp/language/ub">undefined behavior</a>. This is known as the <i>strict aliasing</i> rule and applies to both C++ and C programming languages.
</p>
<p>Note that many C++ compilers relax this rule, as a non-standard language extension, to allow wrong-type access through the inactive member of a <a href="union.html" title="cpp/language/union">union</a> (such access is not undefined in C).
</p>
<p>Also note that this set of rules is more strict than the equivalent rules in the C programming language: C allows access through a pointer to any compatible type. C++ has no compatible types and does not allow access through a pointer or reference to a <a href="data_members.html#Standard_layout" title="cpp/language/data members">layout-compatible type</a> if it doesn't satisfy any of the rules listed above (although access to its member may be allowed)
</p>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Notes">edit</a>]</span> <span class="mw-headline" id="Notes">Notes</span>
</h3>
<p>C++98 did not allow conversion between function pointers and <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span>, this was corrected by DR <a rel="nofollow" class="external text" href="http%3A//www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#195">CWG195</a>
</p>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Example">edit</a>]</span> <span class="mw-headline" id="Example">Example</span>
</h3>
<div class="t-example">
<p> Demonstrates some uses of reinterpret_cast:
 </p>
<div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;cstdint&gt;</span>
<span class="co2">#include &lt;cassert&gt;</span>
<span class="co2">#include &lt;iostream&gt;</span>
<span class="kw4">int</span> f<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> <span class="nu0">42</span><span class="sy4">;</span> <span class="br0">}</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    <span class="kw4">int</span> i <span class="sy1">=</span> <span class="nu0">7</span><span class="sy4">;</span>
 
    <span class="co1">// pointer to integer and back</span>
    uintptr_t v1 <span class="sy1">=</span> <span class="kw1">reinterpret_cast</span><span class="sy1">&lt;</span>uintptr_t<span class="sy1">&gt;</span><span class="br0">(</span><span class="sy3">&amp;</span>i<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// static_cast is an error</span>
    <a href="../io/cout.html"><span class="kw1451">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">"The value of &amp;i is 0x"</span> <span class="sy1">&lt;&lt;</span> <a href="../io/manip/hex.html"><span class="kw1475">std::<span class="me2">hex</span></span></a> <span class="sy1">&lt;&lt;</span> v1 <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
    <span class="kw4">int</span><span class="sy2">*</span> p1 <span class="sy1">=</span> <span class="kw1">reinterpret_cast</span><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy2">*</span><span class="sy1">&gt;</span><span class="br0">(</span>v1<span class="br0">)</span><span class="sy4">;</span>
    <a href="../error/assert.html"><span class="kw622">assert</span></a><span class="br0">(</span>p1 <span class="sy1">==</span> <span class="sy3">&amp;</span>i<span class="br0">)</span><span class="sy4">;</span>
 
    <span class="co1">// pointer to function to another and back</span>
    <span class="kw4">void</span><span class="br0">(</span><span class="sy2">*</span>fp1<span class="br0">)</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">=</span> <span class="kw1">reinterpret_cast</span><span class="sy1">&lt;</span><span class="kw4">void</span><span class="br0">(</span><span class="sy2">*</span><span class="br0">)</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">&gt;</span><span class="br0">(</span>f<span class="br0">)</span><span class="sy4">;</span>
    <span class="co1">// fp1(); undefined behavior</span>
    <span class="kw4">int</span><span class="br0">(</span><span class="sy2">*</span>fp2<span class="br0">)</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">=</span> <span class="kw1">reinterpret_cast</span><span class="sy1">&lt;</span><span class="kw4">int</span><span class="br0">(</span><span class="sy2">*</span><span class="br0">)</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">&gt;</span><span class="br0">(</span>fp1<span class="br0">)</span><span class="sy4">;</span>
    <a href="../io/cout.html"><span class="kw1451">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <a href="../io/manip/hex.html"><span class="kw1474">std::<span class="me2">dec</span></span></a> <span class="sy1">&lt;&lt;</span> fp2<span class="br0">(</span><span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span> <span class="co1">// safe</span>
 
    <span class="co1">// type aliasing through pointer</span>
    <span class="kw4">char</span><span class="sy2">*</span> p2 <span class="sy1">=</span> <span class="kw1">reinterpret_cast</span><span class="sy1">&lt;</span><span class="kw4">char</span><span class="sy2">*</span><span class="sy1">&gt;</span><span class="br0">(</span><span class="sy3">&amp;</span>i<span class="br0">)</span><span class="sy4">;</span>
    <span class="kw1">if</span><span class="br0">(</span>p2<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy1">==</span> <span class="st0">'\x7'</span><span class="br0">)</span>
        <a href="../io/cout.html"><span class="kw1451">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">"This system is little-endian<span class="es1">\n</span>"</span><span class="sy4">;</span>
    <span class="kw1">else</span>
        <a href="../io/cout.html"><span class="kw1451">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">"This system is big-endian<span class="es1">\n</span>"</span><span class="sy4">;</span>
 
    <span class="co1">// type aliasing through reference</span>
    <span class="kw1">reinterpret_cast</span><span class="sy1">&lt;</span><span class="kw4">unsigned</span> <span class="kw4">int</span><span class="sy3">&amp;</span><span class="sy1">&gt;</span><span class="br0">(</span>i<span class="br0">)</span> <span class="sy1">=</span> <span class="nu0">42</span><span class="sy4">;</span>
    <a href="../io/cout.html"><span class="kw1451">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> i <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>Possible output:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">The value of &amp;i is 0x7fff352c3580
42
This system is little-endian
42</pre></div></div> 
</div>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: See also">edit</a>]</span> <span class="mw-headline" id="See_also">See also</span>
</h3>
<table class="t-dsc-begin">

<tr class="t-dsc">
<td>  <a href="const_cast.html" title="cpp/language/const cast"> const_cast conversion </a>
</td>
<td>  adds or removes const
</td>
</tr>

<tr class="t-dsc">
<td>  <a href="static_cast.html" title="cpp/language/static cast"> static_cast conversion </a>
</td>
<td>  performs basic conversions
</td>
</tr>

<tr class="t-dsc">
<td>  <a href="dynamic_cast.html" title="cpp/language/dynamic cast"> dynamic_cast conversion </a>
</td>
<td>  performs checked polymorphic conversions
</td>
</tr>

<tr class="t-dsc">
<td>  <a href="explicit_cast.html" title="cpp/language/explicit cast"> explicit casts </a>
</td>
<td>  permissive conversions between types 
</td>
</tr>

<tr class="t-dsc">
<td>  <a href="implicit_cast.html" title="cpp/language/implicit cast"> standard conversions </a>
</td>
<td>  implicit conversions from one type to another
</td>
</tr>
</table>

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